This invention relates to the manufacture of tires, and, more particularly, to a method and apparatus for the laying of rubber products onto a firm surface or support in the manufacture of tires.
In the manufacture of a tire, various rubber products of different ingredients and properties are used. Such products are referred to as "compound" because they are prepared by the mixing of different base components. The initial preparation is effected by means of tools known as "internal mixers", one example of which is disclosed in U.S. Pat. No. 1,881,994. The compound thus obtained is then worked on calendaring machines and/or extruders (see, for example, U.S. Pat. No. 4,154,536) in order finally to obtain, by means of rolls and/or die blades of suitable dimensions and shape, a semi-finished product in the form of sheets of rubber or strips of small thickness, called flats, or in the form of profiled parts ready to be placed on the tire blank during its manufacture. U.S. Pat. No. 4,299,789 discloses one manner of obtaining a profiled rubber part.
The different semi-finished products thus produced are then assembled to form a raw tire blank, usually on a building drum, examples of which are disclosed in French patent Nos. 1,543,925 and 1,518,250. This method of manufacturing tires, which has been used conventionally in the industry, necessitates the manufacture of a large number of different flats or profiled rubber products in view of the great differences in the structures and dimensions of the tires.
Another reason for dissatisfaction with such prior art processes is the necessity for subjecting the raw rubber products to shaping during the fabrication of the tire. The fabrication ordinarily is carried out on a cylindrical or quasi-cylindrical building drum. By successive deformations, the tire blank approaches its final shape. Some of these rubber products must be capable of withstanding extensive deformations in the raw state. In the raw state, the rubber products must have mechanical properties sufficient to withstand the storage, handling, and laying operations without excessive deformation. All of these requirements result in limitations on the formulation of the rubber compounds, which limitations are dictated only by the process of manufacture of the tire and not by the characteristics of the use of such tire.
U.S. Pat. No. 1,328,006 discloses use of a rigid core instead of a deformable drum as support for the tire blank during its production. However, as the application of semi-finished products of raw rubber onto such a form is even more complicated than the laying of these products on a building drum, this manufacturing technique has been completely abandoned.
Methods which make it possible to eliminate production of semi-finished products of rubber have been described in connection with the recapping of tires. Thus, U.S. Pat No. 3,223,572 describes a method of manufacturing a tread for a recapped tire which consists in suitably winding a large number of turns of a strip of rubber which has been previously prepared independently of the shapes and dimensions of the treads to be reconstituted. However, the precision afforded by this method leaves something to be desired since it is difficult to impart sufficient dimensional stability to such a strip, even by the use of intercalated sheets.
French patent No. 2,091,307 proposes recapping a tire by arranging a die blade having the profile desired for the tread directly on the periphery of the carcass to be capped and extruding rubber across said die blade by means of an extruder, which may be a volumetric extruder, while turning the tire by one revolution in order to obtain a complete tread. This method requires the production of a die blade for each tread profile required, exactly the same as upon the production of treads of semi-finished products.